1. Field of the Invention
The present invention relates to a zoom lens suitable for an image taking optical system used for an image pickup apparatus such as a video camera, a digital still camera, a broadcasting camera and a film camera.
2. Related Background Art
It is requested for image-taking optical systems used for image pickup apparatuses to have a high zoom ratio and a small size as a whole, and further to be capable of reducing a thickness of the image pickup apparatus. Moreover, it is demanded for the image-taking optical systems to have an image stabilization (image blur correction) function to prevent image blur caused by camera shaking.
Zoom lenses have been known each of which includes a reflective member such as a prism being disposed on an optical path and bending (turning) an optical axis of an image-taking optical system by 90 degrees (Japanese Patent Laid-Open Nos. 2007-293051 and 2007-292795).
Moreover, a zoom lens has been known which includes an image stabilization function and is constituted by, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power. In this zoom lens, part of the third lens unit is moved (shifted) in a direction orthogonal to an optical axis to perform image stabilization (U.S. Pat. No. 7,023,624).
The zoom lens disclosed in Japanese Patent Laid-Open No. 2007-293051 is constituted by, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power and a fifth lens unit having a positive refractive power, and includes the reflective member to bend the optical axis further on the image side than the second lens unit. In this zoom lens, the entire third lens unit is moved (shifted) in the direction orthogonal to the optical axis to perform the image stabilization.
The zoom lens disclosed in Japanese Patent Laid-Open No. 2007-292795 is constituted by, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power, and includes the reflective member to bend the optical axis in each of the first and third lens units. In this zoom lens, during zooming, the first and third lens units are fixed (unmoved), and the second and fourth lens units are moved in an optical axis direction. The third lens unit is divided into two partial lens units including an object side lens unit and an image side lens unit which are arranged on both sides of the reflective member. The object side lens unit is moved in the direction orthogonal to the optical axis to perform the image stabilization.
U.S. Pat. No. 7,023,624 discloses a lens configuration in which the third lens unit is divided into a first partial lens unit and a second partial lens unit each having a positive refractive power, and the second partial lens unit is moved in the direction orthogonal to the optical axis to perform the image stabilization.
Applying such a zoom lens including the reflective member to bend the optical axis and having the image stabilization function to an image pickup apparatus makes it easy to reduce the thickness of the image pickup apparatus and to obtain an image with no image blur. However, improper arrangement of the reflective member and the lens unit for the image stabilization makes it difficult to achieve the above-described effects.
For example, in a case of performing the image stabilization by shifting an image stabilizing lens unit adjacent to the reflective member (prism) bending the optical axis by 90 degrees, a large movement amount of a lens holding member holding the image stabilizing lens unit in the direction orthogonal to the optical axis may cause interference between the lens holding member and another lens holding member. Therefore, in a zoom lens in which a lens unit is disposed closely to the reflective member, it is important to appropriately set a configuration of the image stabilizing lens unit.